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{{Other uses}}{{For|an explanation of similar terms|Viridiplantae|Green algae}}{{pp-semi-indef}}{{pp-move-indef}}{{Use dmy dates|date = November 2017}}{{Automatic taxobox| name = Plants! Name(s)! Scope! Description| Green plants, also known as Viridiplantae, Viridiphyta, Chlorobionta or Chloroplastida| Archaeplastida, also known as Plastida or Primoplantae
Mesoproterozoic|present}}| image = Diversity of plants image version 5.png| image_caption =| image_alt =| taxon = Plantae| authority = sensu Copeland, 1956| display_parents = 3| subdivision_ranks = Superdivisions| subdivision = Viridiplantae Cavalier-Smith 1981T. DATE=1981JOURNAL=BIOSYSTEMSISSUE=3–4DOI=10.1016/0303-2647(81)90050-2, 7337818,
  • Chlorobionta Jeffrey 1982, emend. Bremer 1985, emend. Lewis and McCourt 2004JOURNAL, Lewis, L.A., R.M., McCourt, 2004, Green algae and the origin of land plants, American Journal of Botany, 91, 10, 1535–1556, 10.3732/ajb.91.10.1535, 21652308,
  • Chlorobiota Kenrick and Crane 1997BOOK, Kenrick, Paul, Crane, Peter R., 1997, The origin and early diversification of land plants: A cladistic study, Washington, D.C., Smithsonian Institution Press, 978-1-56098-730-7,
  • Chloroplastida Adl et al., 2005 JOURNAL, Adl, S.M., 2005, The new higher level classification of eukaryotes with emphasis on the taxonomy of protists, Journal of Eukaryote Microbiology, 52, 5, 399–451, 10.1111/j.1550-7408.2005.00053.x, etal, 16248873,
  • Phyta Barkley 1939 emend. Holt & Uidica 2007
  • Cormophyta Endlicher, 1836
  • Cormobionta Rothmaler, 1948
  • Euplanta Barkley, 1949
  • Telomobionta Takhtajan, 1964
  • Embryobionta Cronquist et al., 1966
  • Metaphyta Whittaker, 1969
{{hidden end}}}}Plants are mainly multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, plants were treated as one of two kingdoms including all living things that were not animals, and all algae and fungi were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the prokaryotes (the archaea and bacteria). By one definition, plants form the clade Viridiplantae (Latin name for "green plants"), a group that includes the flowering plants, conifers and other gymnosperms, ferns and their allies, hornworts, liverworts, mosses and the green algae, but excludes the red and brown algae.Green plants obtain most of their energy from sunlight via photosynthesis by primary chloroplasts that are derived from endosymbiosis with cyanobacteria. Their chloroplasts contain chlorophylls a and b, which gives them their green color. Some plants are parasitic or mycotrophic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although asexual reproduction is also common.There are about 320 thousand species of plants, of which the great majority, some 260–290 thousand, are seed plants (see the table below).WEB, Numbers of threatened species by major groups of organisms (1996–2010), International Union for Conservation of Nature, 11 March 2010,weblink Green plants provide a substantial proportion of the world's molecular oxygenJOURNAL, Field, C.B., Behrenfeld, M.J., Randerson, J.T., Falkowski, P., 1998, Primary production of the biosphere: Integrating terrestrial and oceanic components, Science (journal), Science, 281, 237–240, 10.1126/science.281.5374.237, 9657713, 5374, 1998Sci...281..237F,weblink and are the basis of most of Earth's ecosystems, especially on land. Plants that produce grain, fruit and vegetables form humankind's basic foods, and have been domesticated for millennia. Plants have many cultural and other uses, as ornaments, building materials, writing material and, in great variety, they have been the source of medicines and psychoactive drugs. The scientific study of plants is known as botany, a branch of biology.

Definition

All living things were traditionally placed into one of two groups, plants and animals. This classification may date from Aristotle (384 BC – 322 BC), who made the distincton between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when Linnaeus (1707–1778) created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these organisms are still often considered plants, particularly in popular contexts.The term "plant" generally implies the possession of the following traits multicellularity, possession of cell walls containing cellulose and the ability to carry out photosynthesis with primary chloroplasts.WEB,weblink plant[2] – Definition from the Merriam-Webster Online Dictionary, 2009-03-25, WEB,weblink plant (life form) -- Britannica Online Encyclopedia, 2009-03-25,

Current definitions of Plantae{{anchor|Current definitions of Plantae}}

When the name Plantae or plant is applied to a specific group of organisms or taxon, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:{| class="wikitable"
Embryophyte>EmbryophytaGlossary of botanical terms#sensu strictissimo>sensu strictissimoPlants in the strictest sense include the liverworts, hornworts, mosses, and vascular plants, as well as fossil plants similar to these surviving groups (e.g., Metaphyta Whittaker, 1969,WHITTAKER YEAR = 1969 URL = HTTP://WWW.IB.USP.BR/INTER/0410113/DOWNLOADS/WHITTAKER_1969.PDF VOLUME = 163 PAGES = 150–160 PMID=5762760 CITESEERX = 10.1.1.403.5430, Plantae Lynn Margulis, 1971MARGULIS YEAR = 1971 URL = VOLUME = 25 PAGES = 242–245 PMID = 28562945, 2406516, ).
Glossary of botanical terms#sensu stricto>sensu strictoPlants in a strict sense include the green algae, and land plants that emerged within them, including stoneworts. The relationships between plant groups are still being worked out, and the names given to them vary considerably. The clade Viridiplantae encompasses a group of organisms that have cellulose in their cell walls, possess chlorophylls a and b and have plastids bound by only two membranes that are capable of photosynthesis and of storing starch. This clade is the main subject of this article (e.g., Plantae Herbert Copeland>Copeland, 1956Copeland, H.F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books, p. 6, weblink.).
Glossary of botanical terms#sensu lato>sensu latoPlants in a broad sense comprise the green plants listed above plus the red algae (Rhodophyta) and the glaucophyte algae (Glaucophyta that store Floridean starch outside the plastids, in the cytoplasm. This clade includes all of the organisms that eons ago acquired their Chloroplast#Primary endosymbiosis>primary chloroplasts directly by engulfing cyanobacteria (e.g., Plantae Cavalier-Smith, 1981CAVALIER-SMITH > FIRST1 = T. TITLE = EUKARYOTE KINGDOMS: SEVEN OR NINE? JOURNAL = BIOSYSTEMS ISSUE = 3–4 DOI=10.1016/0303-2647(81)90050-2, 7337818, ).
List of systems of plant taxonomy>Old definitions of plant (obsolete)Glossary of botanical terms#sensu amplo>sensu amploPlants in the widest sense refers to older, obsolete classifications that placed diverse algae, fungi or bacteria in Plantae (e.g., Plantae or Vegetabilia Linnaeus,Linnaeus, C. (1751). Philosophia botanica, 1st ed., p. 37. Plantae Haeckel 1866,HAECKEL, E. TITLE= GENERALE MORPHOLOGIE DER ORGANISMEN LOCATION= BERLIN, vol. 1: i–xxxii, 1–574, pls I–II; vol. 2: i–clx, 1–462, pls I–VIII, Metaphyta Haeckel, 1894,Haeckel, E. (1894). Die systematische Phylogenie. Plantae Whittaker, 1969).
Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships. These are not yet completely settled, but {{clarify||date=November 2018|text=one accepted relationship between the three groups described above is shown below|reason=which of the references has exactly this cladogram?}}.Based on {{Citation|last=Rogozin |first=I.B. |last2=Basu |first2=M.K.|last3=Csürös |first3=M.|last4=Koonin|first4=E.V. |year=2009 |title=Analysis of Rare Genomic Changes Does Not Support the Unikont–Bikont Phylogeny and Suggests Cyanobacterial Symbiosis as the Point of Primary Radiation of Eukaryotes |journal=Genome Biology and Evolution|pmid=20333181 |volume=1|pmc=2817406|pages=99–113 |doi=10.1093/gbe/evp011 |lastauthoramp=yes}} and {{Citation |last=Becker |first=B. |last2=Marin |first2=B. |year=2009 |title=Streptophyte algae and the origin of embryophytes |journal=Annals of Botany |volume=103 |issue=7 |pages=999–1004 |doi=10.1093/aob/mcp044 |lastauthoramp=yes |pmid=19273476 |pmc=2707909}}; see also the slightly different cladogram in {{Citation |last=Lewis |first=Louise A. |last2=McCourt |first2=R.M. |year=2004 |title=Green algae and the origin of land plants |journal=Am. J. Bot. |volume=91 |issue=10 |pages=1535–1556 |doi=10.3732/ajb.91.10.1535 |lastauthoramp=yes |pmid=21652308}}JOURNAL, Estimating the timing of early eukaryotic diversification with multigene molecular clocks, Proceedings of the National Academy of Sciences, 16 August 2011, 3158185, 21810989, 13624–13629, 108, 33, 10.1073/pnas.1110633108, Laura Wegener, Parfrey, Daniel J.G., Lahr, Andrew H., Knoll, Laura A., Katz, 2011PNAS..10813624P, JOURNAL, Bacterial proteins pinpoint a single eukaryotic root, Proceedings of the National Academy of Sciences, 17 February 2015, 4343179, 25646484, E693–E699, 112, 7, 10.1073/pnas.1420657112, Romain, Derelle, Guifré, Torruella, Vladimír, KlimeÅ¡, Henner, Brinkmann, Eunsoo, Kim, ÄŒestmír, Vlček, B. Franz, Lang, Marek, Eliáš, 2015PNAS..112E.693D, JOURNAL, The Glaucophyta: the blue-green plants in a nutshell, Acta Societatis Botanicorum Poloniae, 1 January 2015, 84, 2, 10.5586/asbp.2015.020, Christopher, Jackson, Susan, Clayden, Adrian, Reyes-Prieto, 149–165, JOURNAL, Sánchez-Baracaldo, Patricia, Raven, John A., Pisani, Davide, Knoll, Andrew H., 12 September 2017, Early photosynthetic eukaryotes inhabited low-salinity habitats, Proceedings of the National Academy of Sciences, 114, 37, E7737–E7745, 10.1073/pnas.1620089114, 28808007, 5603991, JOURNAL, Gitzendanner, Matthew A., Soltis, Pamela S., Wong, Gane K.-S., Ruhfel, Brad R., Soltis, Douglas E., 2018, Plastid phylogenomic analysis of green plants: A billion years of evolutionary history, American Journal of Botany, 105, 3, 291–301, 10.1002/ajb2.1048, 29603143, Those which have been called "plants" are in bold (some minor groups have been omitted).{hide}barlabel|size=8|at=5|label=groups traditionallycalled green algae|cladogram={{cladex|label1=Archaeplastida |1={{cladex
|1=Rhodophyta (red algae)
|2={{cladex
|1=Glaucophyta (glaucophyte algae)
|label2=green plants
|2={{cladex
|1={{cladex
|1=Mesostigmatophyceae|barbegin1=darkgreen
|2={{cladex
|1=Chlorokybophyceae|bar1=darkgreen
|2=Spirotaenia|bar2=darkgreen
{edih}
}}
|2={{cladex
|1=Chlorophyta|bar1=darkgreen
|label2=Streptophyta
|2={{cladex
|1=Charales (stoneworts)|barend1=darkgreen
|2=land plants or embryophytes
}}
}}
}}
}}
}}
}}
}}The way in which the groups of green algae are combined and named varies considerably between authors.

Algae

File:Haeckel Siphoneae.jpg|thumb|Green algae from Ernst Haeckel's Kunstformen der NaturKunstformen der NaturAlgae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The seaweeds range from large multicellular algae to single-celled organisms and are classified into three groups, the green algae, red algae and brown algae. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.BOOK, Margulis, L., 1974, Five-kingdom classification and the origin and evolution of cells, Evolutionary Biology, 7, 45–78, 10.1007/978-1-4615-6944-2_2, 978-1-4615-6946-6, The Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common; primary chloroplasts derived from cyanobacteria containing chlorophylls a and b, cell walls containing cellulose, and food stores in the form of starch contained within the plastids. They undergo closed mitosis without centrioles, and typically have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria.Two additional groups, the Rhodophyta (red algae) and Glaucophyta (glaucophyte algae), also have primary chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour. These groups also differ from green plants in that the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event. This is the broadest modern definition of the term 'plant'.In contrast, most other algae (e.g. brown algae/diatoms, haptophytes, dinoflagellates, and euglenids) not only have different pigments but also have chloroplasts with three or four surrounding membranes. They are not close relatives of the Archaeplastida, presumably having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in even the broadest modern definition of the plant kingdom, although they were in the past.The green plants or Viridiplantae were traditionally divided into the green algae (including the stoneworts) and the land plants. However, it is now known that the land plants evolved from within a group of green algae, so that the green algae by themselves are a paraphyletic group, i.e. a group that excludes some of the descendants of a common ancestor. Paraphyletic groups are generally avoided in modern classifications, so that in recent treatments the Viridiplantae have been divided into two clades, the Chlorophyta and the Streptophyta (including the land plants and Charophyta).{{Citation |last=Lewis |first=Louise A. |last2=McCourt |first2=R.M. |year=2004 |title=Green algae and the origin of land plants |journal=Am. J. Bot. |volume=91 |issue=10 |pages=1535–1556 |doi=10.3732/ajb.91.10.1535 |lastauthoramp=yes |pmid=21652308}}{{Citation |last=Becker |first=B. |last2=Marin |first2=B. |year=2009 |title=Streptophyte algae and the origin of embryophytes |journal=Annals of Botany |volume=103 |issue=7 |pages=999–1004 |doi=10.1093/aob/mcp044 |lastauthoramp=yes |pmid=19273476 |pmc=2707909}}The Chlorophyta (a name that has also been used for all green algae) are the sister group to the Charophytes, from which the land plants evolved. There are about 4,300 species,WEB,weblink AlgaeBase version 4.2 World-wide electronic publication, National University of Ireland, Galway, 2007-09-23, Phylum: Chlorophyta taxonomy browser, Guiry, M.D., Guiry, G.M., 2007, mainly unicellular or multicellular marine organisms such as the sea lettuce, Ulva.The other group within the Viridiplantae are the mainly freshwater or terrestrial Streptophyta, which consists of the land plants together with the Charophyta, itself consisting of several groups of green algae such as the desmids and stoneworts. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched. The genus Spirogyra is a filamentous streptophyte alga familiar to many, as it is often used in teaching and is one of the organisms responsible for the algal "scum" on ponds. The freshwater stoneworts strongly resemble land plants and are believed to be their closest relatives.{{citation needed|date=March 2017}} Growing immersed in fresh water, they consist of a central stalk with whorls of branchlets.

Fungi

Linnaeus' original classification placed the fungi within the Plantae, since they were unquestionably neither animals or minerals and these were the only other alternatives. With 19th century developments in microbiology, Ernst Haeckel introduced the new kingdom Protista in addition to Plantae and Animalia, but whether fungi were best placed in the Plantae or should be reclassified as protists remained controversial. In 1969, Robert Whittaker proposed the creation of the kingdom Fungi. Molecular evidence has since shown that the most recent common ancestor (concestor), of the Fungi was probably more similar to that of the Animalia than to that of Plantae or any other kingdom.BOOK, Deacon, J.W., 2005, Fungal Biology, Wiley, 978-1-4051-3066-0,weblink Whittaker's original reclassification was based on the fundamental difference in nutrition between the Fungi and the Plantae. Unlike plants, which generally gain carbon through photosynthesis, and so are called autotrophs, fungi do not possess chloroplasts and generally obtain carbon by breaking down and absorbing surrounding materials, and so are called heterotrophic saprotrophs. In addition, the substructure of multicellular fungi is different from that of plants, taking the form of many chitinous microscopic strands called hyphae, which may be further subdivided into cells or may form a syncytium containing many eukaryotic nuclei. Fruiting bodies, of which mushrooms are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.{{cn|date=November 2018}}

Diversity

The table below shows some species count estimates of different green plant (Viridiplantae) divisions. It suggests there are about 300,000 species of living Viridiplantae, of which 85–90% are flowering plants. (Note: as these are from different sources and different dates, they are not necessarily comparable, and like all species counts, are subject to a degree of uncertainty in some cases.){| class="wikitable" style="float:left; margin-left:1em;"|+Diversity of living green plant (Viridiplantae) divisions! style="background:lightgreen; text-align:center;"| Informal group! style="background:lightgreen; text-align:center;"| Division name! style="background:lightgreen; text-align:center;"| Common name! style="background:lightgreen; text-align:center;"| No. of living species! style="background:lightgreen; text-align:center;"| Approximate No. in informal group Green algae| Chlorophyta green algae (chlorophytes) 3,800–4,300 Van den Hoek, C.; Mann, D.G.; & Jahns, H.M. 1995. Algae: An Introduction to Phycology. pp. 343, 350, 392, 413, 425, 439, & 448 (Cambridge: Cambridge University Press). {{ISBNlast=Guiry last2=Guiry year=2011 publisher=World-wide electronic publication, National University of Ireland, Galway accessdate=2011-07-26 |lastauthoramp=yes }} 8,500(6,600–10,300)| Charophyta green algae (e.g. desmids & stoneworts) 2,800–6,000 {{Citation first=M.D. first2=G.M. title=AlgaeBase : Charophyta url=http://www.algaebase.org/browse/taxonomy/?searching=true&gettaxon=Charophyta lastauthoramp=yes }}Van den Hoek, C.; Mann, D.G.; & Jahns, H.M. 1995. Algae: An Introduction to Phycology. pp. 457, 463, & 476. (Cambridge: Cambridge University Press). {{ISBN|0-521-30419-9}} Bryophytes| Marchantiophyta liverworts 6,000–8,000 Crandall-Stotler, Barbara & Stotler, Raymond E., 2000. "Morphology and classification of the Marchantiophyta". p. 21 in A. Jonathan Shaw & Bernard Goffinet (Eds.), Bryophyte Biology. (Cambridge: Cambridge University Press). {{ISBN|0-521-66097-1}} 19,000(18,100–20,200)| Anthocerotophyta hornworts 100–200 Schuster, Rudolf M., The Hepaticae and Anthocerotae of North America, volume VI, pp. 712–713. (Chicago: Field Museum of Natural History, 1992). {{ISBN|0-914868-21-7}}.Moss>Bryophyta mosses 12,000 GOFFINET >FIRST= BERNARD YEAR=2004 JOURNAL=MONOGRAPHS IN SYSTEMATIC BOTANY PAGES=205–239, Pteridophytes| Lycopodiophyta club mosses 1,200 RAVEN >FIRST=PETER H. LAST2=EVERT LAST3=EICHHORN TITLE=BIOLOGY OF PLANTS LOCATION=NEW YORK ISBN=978-0-7167-1007-3, 12,000(12,200)Fern>Pteridophyta ferns, whisk ferns & horsetails 11,000 Seed plants| Cycadophyta cycads 160 GIFFORD >FIRST=ERNEST M. LAST2=FOSTER TITLE=MORPHOLOGY AND EVOLUTION OF VASCULAR PLANTS PAGE=358 PUBLISHER=W.H. FREEMAN AND COMPANY, 978-0-7167-1946-5, 260,000(259,511)| Ginkgophyta ginkgo 1 TAYLOR >FIRST=THOMAS N. LAST2=TAYLOR TITLE=THE BIOLOGY AND EVOLUTION OF FOSSIL PLANTS LOCATION=NEW JERSEY ISBN=978-0-13-651589-0, | Pinophyta conifers 630 | Gnetophyta gnetophytes 70 Flowering plant>Magnoliophyta flowering plants 258,650 International Union for Conservation of Nature and Natural Resources, 2006. IUCN Red List of Threatened Species:Summary Statistics{{Clear}}The naming of plants is governed by the International Code of Nomenclature for algae, fungi, and plants and International Code of Nomenclature for Cultivated Plants (see cultivated plant taxonomy).

Evolution

{{further|Evolutionary history of plants}}The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today. Plants in all of these groups continue to thrive, especially in the environments in which they evolved.An algal scum formed on the land {{Ma|1200}}, but it was not until the Ordovician Period, around {{Ma|450}}, that land plants appeared."The oldest fossils reveal evolution of non-vascular plants by the middle to late Ordovician Period (≈450–440 m.y.a.) on the basis of fossil spores" Transition of plants to land {{webarchive|url=https://web.archive.org/web/20080302040410weblink |date=2 March 2008 }} However, new evidence from the study of carbon isotope ratios in Precambrian rocks has suggested that complex photosynthetic plants developed on the earth over 1000 m.y.a.JOURNAL, Strother, Paul K., Battison, Leila, Brasier, Martin D., Wellman, Charles H., 26 May 2011, Earth's earliest non-marine eukaryotes, Nature (journal), Nature, 473, 7348, 505–509, 10.1038/nature09943, 21490597, 2011Natur.473..505S, For more than a century it has been assumed that the ancestors of land plants evolved in aquatic environments and then adapted to a life on land, an idea usually credited to botanist Frederick Orpen Bower in his 1908 book "The Origin of a Land Flora". A recent alternative view, supported by genetic evidence, is that they evolved from terrestrial single-celled algae,JOURNAL, Harholt, Jesper, Moestrup, Øjvind, Ulvskov, Peter, 1 February 2016, Why Plants Were Terrestrial from the Beginning,weblink Trends (journals), Trends in Plant Science, 21, 2, 96–101, 10.1016/j.tplants.2015.11.010, 26706443, and that even the common ancestor of red and green algae, and the unicellular freshwater algae glaucophytes, originated in a terrestrial environment in freshwater biofilms or microbial mats.An early-branching freshwater cyanobacterium at the origin of plastids - NCBI Primitive land plants began to diversify in the late Silurian Period, around {{Ma|420}}, and the results of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs. By the middle of the Devonian Period most of the features recognised in plants today are present, including roots, leaves and secondary wood, and by late Devonian times seeds had evolved.JOURNAL, Rothwell, G.W., Scheckler, S.E., Gillespie, W.H., 1989, Elkinsia gen. nov., a Late Devonian gymnosperm with cupulate ovules, Botanical Gazette, 150, 2, 170–189, 10.1086/337763, 2995234, Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees. Evolutionary innovation continued in the Carboniferous and later geological periods and is ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the evolution of flowering plants in the Triassic (~{{ma|200}}), which exploded in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around {{Ma|40}}. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low {{co2}} and warm, dry conditions of the tropics over the last {{Ma|10|million years}}.A 1997 proposed phylogenetic tree of Plantae, after Kenrick and Crane,Kenrick, Paul & Peter R. Crane. 1997. The Origin and Early Diversification of Land Plants: A Cladistic Study. (Washington, D.C., Smithsonian Institution Press.) {{ISBN|1-56098-730-8}}. is as follows, with modification to the Pteridophyta from Smith et al.JOURNAL, Smith Alan R., Pryer, Kathleen M., Schuettpelz, E., Korall, P., Schneider, H., Wolf, Paul G., A classification for extant ferns, 2006, Taxon, 55, 3, 705–731,weblink 10.2307/25065646, yes,weblink" title="web.archive.org/web/20080226232147weblink">weblink 26 February 2008, 25065646, The Prasinophyceae are a paraphyletic assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta: later authors have not followed this suggestion.{hide}clade| style=font-size:75%;line-height:75%;|1={{clade
|1=Prasinophyceae (micromonads)
|2={{clade
|label1=Streptobionta
|1={{clade
|1={{clade
|label1=Embryophytes
|1={{clade
|1={{clade
|label1=Stomatophytes
|1={{clade
|1={{clade
|label1=Polysporangiates
|1={{clade
|1={{clade
|label1=Tracheophytes
|1={{clade


|label1=Eutracheophytes
|1={{clade
|label1=Euphyllophytina
|1={{clade
|label1=Lignophyta
|1={{clade
|1=Spermatophytes (seed plants)
|2=Progymnospermophyta â€ 
{edih}
|label2=Pteridophyta
|2={{clade
|1={{clade
|1=Pteridopsida (true ferns)
|2=Marattiopsida
|3=Equisetopsida (horsetails)
|4=Psilotopsida (whisk ferns & adders'-tongues)
|5=Cladoxylopsida â€ 
}}
}}
}}
|label2=Lycophytina
|2={{clade
|1=Lycopodiophyta
|2=Zosterophyllophyta â€ 
}}
}}
|2=Rhyniophyta â€ 


}}
}}
|2=Aglaophyton â€ 
|3=Horneophytopsida â€ 
}}
}}
|2=Bryophyta (mosses)
|3=Anthocerotophyta (hornworts)
}}
}}
|2=Marchantiophyta (liverworts)
}}
}}
|2=Charophyta
}}
}}
|3={{clade
|label1=Chlorophyta
|1={{clade
|1={{clade
|1=Trebouxiophyceae (Pleurastrophyceae)
|2=Chlorophyceae
}}
|2=Ulvophyceae
}}
}}
}}
}}A newer proposed classification follows Leliaert et al. 2011JOURNAL, Leliaert, Frederik, Verbruggen, Heroen, Zechman, Frederick W., Into the deep: New discoveries at the base of the green plant phylogeny, BioEssays, 33, 9, 2011, 683–692, 10.1002/bies.201100035, 21744372, and modified with Silar 2016{{citation | date=2016| author = Silar, Philippe | title = Protistes Eucaryotes: Origine, Evolution et Biologie des Microbes Eucaryotes| url=https://hal.archives-ouvertes.fr/hal-01263138 |pages=1–462 |journal=HAL Archives-ouvertes}}JOURNAL, Mikhailyuk, Tatiana, Lukešová, Alena, Glaser, Karin, Holzinger, Andreas, Obwegeser, Sabrina, Nyporko, Svetlana, Friedl, Thomas, Karsten, Ulf, 2018, New Taxa of Streptophyte Algae (Streptophyta) from Terrestrial Habitats Revealed Using an Integrative Approach, Protist, 169, 3, 406–431, 10.1016/j.protis.2018.03.002, 29860113, 6071840, 1434-4610, for the green algae clades and Novíkov & Barabaš-Krasni 2015BOOK, Novíkov & Barabaš-Krasni, 2015, Modern plant systematics, 685, Liga-Pres, 978-966-397-276-3, 10.13140/RG.2.1.4745.6164,weblink for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.{{barlabel |size=1 |at=0.1 |label=Green algae|cladogram={hide}clade| style=font-size:90%;line-height:80%;|label1=Viridiplantae|1={{cladex
|1= {{cladex|barbegin1=darkgreen
|1=Mesostigmatophyceae
|2={{cladex
|1=Chlorokybophyceae |bar1=darkgreen
|2=Spirotaenia|bar2=darkgreen
{edih}
}}
|2={{cladex
|label1=Chlorobionta
|1=Chlorophyta inc. Prasinophyceae |bar1=darkgreen
|label2=Streptobionta
|2={{cladex
|1=Streptofilum |bar1=darkgreen
|2={{cladex
|1=Klebsormidiophyta |bar1=darkgreen
|label2=Phragmoplastophyta
|2={{cladex
|1=Charophyta Rabenhorst 1863 emend. Lewis & McCourt 2004 (Stoneworts)|bar1=darkgreen
|2={{cladex
|1=Coleochaetophyta |bar1=darkgreen
|2={{cladex
|1=Zygnematophyta|barend1=darkgreen
|label2=Embryobiotes
|2={{cladex
|1=Marchantiophyta (Liverworts)
|label2=Stomatophyta
|2={{cladex
|1=Bryophyta (True mosses)
|2={{cladex
|1=Anthocerotophyta (Non-flowering hornworts)
|label2=Polysporangiophyta
|2={{cladex
|1=†Horneophyta
|2={{cladex
|1=†Aglaophyta
|2=Tracheophyta (Vascular Plants)
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}}}

Embryophytes

File:Ferns02.jpg|thumb|Dicksonia antarctica, a species of tree ferntree fern{{unreferenced section|date=November 2018}}The plants that are likely most familiar to us are the multicellular land plants, called embryophytes. Embryophytes include the vascular plants, such as ferns, conifers and flowering plants. They also include the bryophytes, of which mosses and liverworts are the most common.All of these plants have eukaryotic cells with cell walls composed of cellulose, and most obtain their energy through photosynthesis, using light, water and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are parasites on other species of photosynthetic plants. Embryophytes are distinguished from green algae, which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.Bryophytes first appeared during the early Paleozoic. They mainly live in habitats where moisture is available for significant periods, although some species, such as Targionia, are desiccation-tolerant. Most species of bryophytes remain small throughout their life-cycle. This involves an alternation between two generations: a haploid stage, called the gametophyte, and a diploid stage, called the sporophyte. In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The embryophytes have the ability to secrete a cuticle on their outer surface, a waxy layer that confers resistant to desiccation. In the mosses and hornworts a cuticle is usually only produced on the sporophyte. Stomata are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange.Vascular plants first appeared during the Silurian period, and by the Devonian had diversified and spread into many different terrestrial environments. They developed a number of adaptations that allowed them to spread into increasingly more arid places, notably the vascular tissues xylem and phloem, that transport water and food throughout the organism. Root systems capable of obtaining soil water and nutrients also evolved during the Devonian. In modern vascular plants, the sporophyte is typically large, branched, nutritionally independent and long-lived, but there is increasing evidence that Paleozoic gametophytes were just as complex as the sporophytes. The gametophytes of all vascular plant groups evolved to become reduced in size and prominence in the life cycle.In seed plants, the microgametophyte is reduced from a multicellular free-living organism to a few cells in a pollen grain and the miniaturised megagametophyte remains inside the megasporangium, attached to and dependent on the parent plant. A megasporangium enclosed in a protective layer called an integument is known as an ovule. After fertilisation by means of sperm produced by pollen grains, an embryo sporophyte develops inside the ovule. The integument becomes a seed coat, and the ovule develops into a seed. Seed plants can survive and reproduce in extremely arid conditions, because they are not dependent on free water for the movement of sperm, or the development of free living gametophytes.The first seed plants, pteridosperms (seed ferns), now extinct, appeared in the Devonian and diversified through the Carboniferous. They were the ancestors of modern gymnosperms, of which four surviving groups are widespread today, particularly the conifers, which are dominant trees in several biomes. The name gymnosperm comes from the Greek composite word γυμνόσπερμος (γυμνός gymnos, "naked" and σπέρμα sperma, "seed"), as the ovules and subsequent seeds are not enclosed in a protective structure (carpels or fruit), but are borne naked, typically on cone scales.

Fossils

File:Petrified forest log 1 md.jpg|thumb|upright|A petrified log in Petrified Forest National ParkPetrified Forest National Park{{refimprove section|date=November 2018}}Plant fossils include roots, wood, leaves, seeds, fruit, pollen, spores, phytoliths, and amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. Pollen, spores and algae (dinoflagellates and acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the Cambrian. These fossils resemble calcified multicellular members of the Dasycladales. Earlier Precambrian fossils are known that resemble single-cell green algae, but definitive identity with that group of algae is uncertain.The earliest fossils attributed to green algae date from the Precambrian (ca. 1200 mya).BOOK, Knoll, Andrew H, Life on a Young Planet: The First Three Billion Years of Evolution on Earth, Princeton University Press, 2003, BOOK, Tappan, H, Palaeobiology of Plant Protists, Freeman, San Francisco, 1980, The resistant outer walls of prasinophyte cysts (known as phycomata) are well preserved in fossil deposits of the Paleozoic (ca. 250–540 mya). A filamentous fossil (Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the Cladophorales, while the oldest reliable records of the Bryopsidales, Dasycladales) and stoneworts are from the Paleozoic.JOURNAL, Leliaert, F., Smith, D.R., Moreau, H., Herron, M.D., Verbruggen, H., Delwiche, C.F., De Clerck, O., 2012, Phylogeny and molecular evolution of the green algae,weblink 10.1080/07352689.2011.615705, Critical Reviews in Plant Sciences, 31, 1–46, yes,weblink" title="web.archive.org/web/20150626102452weblink">weblink 26 June 2015, JOURNAL, Butterfield, Nicholas J., Knoll, Andrew H., Swett, Keene, Paleobiology of the Neoproterozoic Svanbergfjellet Formation, Spitsbergen, Lethaia, 27, 1, 1994, 76, 10.1111/j.1502-3931.1994.tb01558.x, The oldest known fossils of embryophytes date from the Ordovician, though such fossils are fragmentary. By the Silurian, fossils of whole plants are preserved, including the simple vascular plant Cooksonia in mid-Silurian and the much larger and more complex lycophyte Baragwanathia longifolia in late Silurian. From the early Devonian Rhynie chert, detailed fossils of lycophytes and rhyniophytes have been found that show details of the individual cells within the plant organs and the symbiotic association of these plants with fungi of the order Glomales. The Devonian period also saw the evolution of leaves and roots, and the first modern tree, Archaeopteris. This tree with fern-like foliage and a trunk with conifer-like wood was heterosporous producing spores of two different sizes, an early step in the evolution of seeds.BOOK, Wilson A., Stewart, Gar W., Rothwell, Paleobotany and the evolution of plants, 2, 1993, Cambridge University Press, 978-0521382946, The Coal measures are a major source of Paleozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Grove at Victoria Park in Glasgow, Scotland, the stumps of Lepidodendron trees are found in their original growth positions.The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the Mesozoic and Cenozoic eras. Sequoia and its allies, magnolia, oak, and palms are often found.Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by erosion. Petrified wood is often heavily silicified (the organic material replaced by silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using lapidary equipment. Fossil forests of petrified wood have been found in all continents.Fossils of seed ferns such as Glossopteris are widely distributed throughout several continents of the Southern Hemisphere, a fact that gave support to Alfred Wegener's early ideas regarding Continental drift theory.

Structure, growth and development

{{further|Plant morphology}}File:Leaf 1 web.jpg|thumb|The leaf is usually the primary site of photosynthesisphotosynthesisMost of the solid material in a plant is taken from the atmosphere. Through the process of photosynthesis, most plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars. These sugars are then used as building blocks and form the main structural component of the plant. Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process; it is generally present in plant leaves, and often in other plant parts as well. Parasitic plants, on the other hand, use the resources of their host to provide the materials needed for metabolism and growth.Plants usually rely on soil primarily for support and water (in quantitative terms), but they also obtain compounds of nitrogen, phosphorus, potassium, magnesium and other elemental nutrients from the soil. Epiphytic and lithophytic plants depend on air and nearby debris for nutrients, and carnivorous plants supplement their nutrient requirements, particularly for nitrogen and phosphorus, with insect prey that they capture. For the majority of plants to grow successfully they also require oxygen in the atmosphere and around their roots (soil gas) for respiration. Plants use oxygen and glucose (which may be produced from stored starch) to provide energy.BOOK, Life on Earth, 1973, 978-0-87893-934-3, 145, Wilson, Edward O., Edward O. Wilson, First, etal, Some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as mangroves and reed (Phragmites australis),JOURNAL, Crawford, R.M.M., 1982, Physiological responses in flooding, Encyclopedia of Plant Physiology, 12B, 453–477, can grow with their roots in anoxic conditions.

Factors affecting growth

The genome of a plant controls its growth. For example, selected varieties or genotypes of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.Robbins, W.W.; Weier, T.E.; et al., Botany: Plant Science, 3rd edition, Wiley International, New York, 1965.Growth is also determined by environmental factors, such as temperature, available water, available light, carbon dioxide and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth and the timing of its development.{{cn|date=November 2018}}Biotic factors also affect plant growth. Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of mycorrhizal fungi, and attacks by insects or plant diseases, including those caused by bacteria, fungi, viruses, and nematodes.(File:Eenbruinigherfstblad.jpg|thumb|left|There is no photosynthesis in deciduous leaves in autumn.)Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Annual plants grow and reproduce within one growing season, biennial plants grow for two growing seasons and usually reproduce in second year, and perennial plants live for many growing seasons and once mature will often reproduce annually. These designations often depend on climate and other environmental factors. Plants that are annual in alpine or temperate regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both evergreens that keep their leaves the entire year, and deciduous plants that lose their leaves for some part of it. In temperate and boreal climates, they generally lose their leaves during the winter; many tropical plants lose their leaves during the dry season.{{cn|date=November 2018}}The growth rate of plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025-0.250 mm/h. Some climbing species, such as kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.{{cn|date=November 2018}}Plants protect themselves from frost and dehydration stress with antifreeze proteins, heat-shock proteins and sugars (sucrose is common). LEA (Late Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of desiccation and freezing.JOURNAL, Goyal, K., Walton, L.J., Tunnacliffe, A., LEA proteins prevent protein aggregation due to water stress, Biochemical Journal, 2005, 388, Part 1, 151–157, 15631617, 10.1042/BJ20041931, 1186703,

Effects of freezing

When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs within cells (intracellularly) or outside cells in intercellular spaces.Glerum, C. 1985. Frost hardiness of coniferous seedlings: principles and applications. pp. 107–123 in Duryea, M.L. (Ed.). Proceedings: Evaluating seedling quality: principles, procedures, and predictive abilities of major tests. Workshop, October 1984, Oregon State Univ., For. Res. Lab., Corvallis OR. Intracellular freezing, which usually kills the cellLyons, J.M.; Raison, J.K.; Steponkus, P.L. 1979. The plant membrane in response to low temperature: an overview. pp. 1–24 in Lyons, J.M.; Graham, D.; Raison, J.K. (Eds.). Low Temperature Stress in Crop Plants. Academic Press, New York NY. regardless of the hardiness of the plant and its tissues, seldom occurs in nature because rates of cooling are rarely high enough to support it. Rates of cooling of several degrees Celsius per minute are typically needed to cause intracellular formation of ice.Mazur, P. 1977. The role of intracellular freezing in the death of cells cooled at supraoptimal rates. Cryobiology 14:251–272. At rates of cooling of a few degrees Celsius per hour, segregation of ice occurs in intercellular spaces.Sakai, A.; Larcher, W. (Eds.) 1987. Frost Survival of Plants. Springer-Verlag, New York. 321 p. This may or may not be lethal, depending on the hardiness of the tissue. At freezing temperatures, water in the intercellular spaces of plant tissue freezes first, though the water may remain unfrozen until temperatures drop below {{convert|-7|C|F}}. After the initial formation of intercellular ice, the cells shrink as water is lost to the segregated ice, and the cells undergo freeze-drying. This dehydration is now considered the fundamental cause of freezing injury.

DNA damage and repair

Plants are continuously exposed to a range of biotic and abiotic stresses. These stresses often cause DNA damage directly, or indirectly via the generation of reactive oxygen species.JOURNAL, Roldán-Arjona, T., Ariza, R.R., Repair and tolerance of oxidative DNA damage in plants, Mutation Research, 681, 2–3, 169–179, 2009, 18707020, 10.1016/j.mrrev.2008.07.003, Plants are capable of a DNA damage response that is a critical mechanism for maintaining genome stability.JOURNAL, Yoshiyama, K.O., SOG1: a master regulator of the DNA damage response in plants, Genes and Genetic Systems, 90, 4, 209–216, 2016, 26617076, 10.1266/ggs.15-00011, The DNA damage response is particularly important during seed germination, since seed quality tends to deteriorate with age in association with DNA damage accumulation.JOURNAL, Waterworth, W.M., Bray, C.M., West, C.E., The importance of safeguarding genome integrity in germination and seed longevity, Journal of Experimental Botany, 66, 12, 3549–3558, 2015, 25750428, 10.1093/jxb/erv080, During germination repair processes are activated to deal with this accumulated DNA damage.JOURNAL, Koppen, G., Verschaeve, L., The alkaline single-cell gel electrophoresis/comet assay: a way to study DNA repair in radicle cells of germinating Vicia faba, Folia Biologica (Prague), 47, 2, 50–54, 2001, 11321247, In particular, single- and double-strand breaks in DNA can be repaired.JOURNAL, Waterworth, W.M., Masnavi, G., Bhardwaj, R.M., Jiang, Q., Bray, C.M., West, C.E., A plant DNA ligase is an important determinant of seed longevity, Plant Journal, 63, 5, 848–860, 2010, 20584150, 10.1111/j.1365-313X.2010.04285.x, The DNA checkpoint kinase ATM has a key role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.JOURNAL, Waterworth, W.M., Footitt, S., Bray, C.M., Finch-Savage, W.E., West, C.E., DNA damage checkpoint kinase ATM regulates germination and maintains genome stability in seeds, PNAS, 113, 34, 9647–9652, 2016, 27503884, 5003248, 10.1073/pnas.1608829113,

Plant cells

(File:Plant cell structure-en.svg|thumb|Plant cell structure)Plant cells are typically distinguished by their large water-filled central vacuole, chloroplasts, and rigid cell walls that are made up of cellulose, hemicellulose, and pectin. Cell division is also characterized by the development of a phragmoplast for the construction of a cell plate in the late stages of cytokinesis. Just as in animals, plant cells differentiate and develop into multiple cell types. Totipotent meristematic cells can differentiate into vascular, storage, protective (e.g. epidermal layer), or reproductive tissues, with more primitive plants lacking some tissue types.Campbell, Reece, Biology, 7th edition, Pearson/Benjamin Cummings, 2005.

Physiology

Photosynthesis

Plants are photosynthetic, which means that they manufacture their own food molecules using energy obtained from light. The primary mechanism plants have for capturing light energy is the pigment chlorophyll. All green plants contain two forms of chlorophyll, chlorophyll a and chlorophyll b. The latter of these pigments is not found in red or brown algae.The simple equation of photosynthesis is as follows:6CO2{} + 6H2O{} ->[text{in the presence of light and chlorophyll}] C6H12O6{} + 6O2{}

Immune system

{{See also|Immune system|Plant disease resistance}}By means of cells that behave like nerves, plants receive and distribute within their systems information about incident light intensity and quality. Incident light that stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a bundle sheath cell. Researchers, from the Warsaw University of Life Sciences in Poland, found that plants have a specific memory for varying light conditions, which prepares their immune systems against seasonal pathogens.NEWS,weblink Plants 'can think and remember', Victoria, Gill, 14 July 2010, www.bbc.co.uk, BBC News, Plants use pattern-recognition receptors to recognize conserved microbial signatures. This recognition triggers an immune response. The first plant receptors of conserved microbial signatures were identified in rice (XA21, 1995)JOURNAL, Song, W.Y., A receptor kinase-like protein encoded by the rice disease resistance gene, XA21, Science, 270, 5243, 1804–1806, 1995, 8525370, 10.1126/science.270.5243.1804, etal, 1995Sci...270.1804S,weblink and in Arabidopsis thaliana (FLS2, 2000).JOURNAL, Gomez-Gomez, L., FLS2: an LRR receptor-like kinase involved in the perception of the bacterial elicitor flagellin in Arabidopsis, Molecular Cell, 5, 6, 1003–1011, 2000, 10911994, 10.1016/S1097-2765(00)80265-8, etal, Plants also carry immune receptors that recognize highly variable pathogen effectors. These include the NBS-LRR class of proteins.

Internal distribution

Vascular plants differ from other plants in that nutrients are transported between their different parts through specialized structures, called xylem and phloem. They also have roots for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.

Genomics

Plants have some of the largest genomes among all organisms.JOURNAL, Michael, Todd P., Jackson, Scott, 1 July 2013, The First 50 Plant Genomes, The Plant Genome, 6, 2, 0, 10.3835/plantgenome2013.03.0001in, The largest plant genome (in terms of gene number) is that of wheat (Triticum asestivum), predicted to encode ≈94,000 genesJOURNAL, Brenchley, Rachel, Spannagl, Manuel, Pfeifer, Matthias, Barker, Gary L.A., D'Amore, Rosalinda, Allen, Alexandra M., McKenzie, Neil, Krame r, Melissa, Kerhornou, Arnau, 29 November 2012, Analysis of the bread wheat genome using whole-genome shotgun sequencing, Nature, 491, 7426, 705–710, 10.1038/nature11650, 3510651, 23192148, 2012Natur.491..705B, and thus almost 5 times as many as the human genome. The first plant genome sequenced was that of Arabidopsis thaliana which encodes about 25,500 genes.JOURNAL, Arabidopsis Genome Initiative, 14 December 2000, Analysis of the genome sequence of the flowering plant Arabidopsis thaliana, Nature, 408, 6814, 796–815, 10.1038/35048692, 11130711, 2000Natur.408..796T, In terms of sheer DNA sequence, the smallest published genome is that of the carnivorous bladderwort (Utricularia gibba) at 82 Mb (although it still encodes 28,500 genes)JOURNAL, Ibarra-Laclette, Enrique, Lyons, Eric, Hernández-Guzmán, Gustavo, Pérez-Torres, Claudia Anahí, Carretero-Paulet, Lorenzo, Chang, Tien-Hao, Lan, Tianying, Welch, Andreanna J., Juárez, María Jazmín Abraham, 6 June 2013, Architecture and evolution of a minute plant genome, Nature, 498, 7452, 94–98, 10.1038/nature12132, 4972453, 23665961, 2013Natur.498...94I, while the largest, from the Norway Spruce (Picea abies), extends over 19,600 Mb (encoding about 28,300 genes).JOURNAL, Nystedt, Björn, Street, Nathaniel R., Wetterbom, Anna, Zuccolo, Andrea, Lin, Yao-Cheng, Scofield, Douglas G., Vezzi, Francesco, Delhomme, Nicolas, Giacomello, Stefania, 30 May 2013, The Norway spruce genome sequence and conifer genome evolution, Nature, 497, 7451, 579–584, 10.1038/nature12211, 23698360, 2013Natur.497..579N,

Ecology

The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis, at first by cyanobacteria and later by photosynthetic eukaryotes, radically changed the composition of the early Earth's anoxic atmosphere, which as a result is now 21% oxygen. Animals and most other organisms are aerobic, relying on oxygen; those that do not are confined to relatively rare anaerobic environments. Plants are the primary producers in most terrestrial ecosystems and form the basis of the food web in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.{{cn|date=November 2018}}Land plants are key components of the water cycle and several other biogeochemical cycles. Some plants have coevolved with nitrogen fixing bacteria, making plants an important part of the nitrogen cycle. Plant roots play an essential role in soil development and the prevention of soil erosion.{{cn|date=November 2018}}

Distribution

Plants are distributed almost worldwide. While they inhabit a multitude of biomes and ecoregions, few can be found beyond the tundras at the northernmost regions of continental shelves. At the southern extremes, plants of the Antarctic flora have adapted tenaciously to the prevailing conditions.{{cn|date=November 2018}}Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such as grasslands, taiga and tropical rainforest.{{cn|date=November 2018}}

Ecological relationships

File:Venus Flytrap showing trigger hairs.jpg|thumb|The Venus flytrap, a species of carnivorous plantcarnivorous plant{{refimprove section|date=November 2018}}Numerous animals have coevolved with plants. Many animals pollinate flowers in exchange for food in the form of pollen or nectar. Many animals disperse seeds, often by eating fruit and passing the seeds in their feces. Myrmecophytes are plants that have coevolved with ants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from herbivores and sometimes competing plants. Ant wastes provide organic fertilizer.The majority of plant species have various kinds of fungi associated with their root systems in a kind of mutualistic symbiosis known as mycorrhiza. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for endophytic fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, Neotyphodium coenophialum, in tall fescue (Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S.Various forms of parasitism are also fairly common among plants, from the semi-parasitic mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic broomrape and toothwort that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Some plants, known as myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as epiparasites on other plants.Many plants are epiphytes, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. Hemiepiphytes like the strangler fig begin as epiphytes but eventually set their own roots and overpower and kill their host. Many orchids, bromeliads, ferns and mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata that may contain complex aquatic food webs.Frank, Howard, Bromeliad Phytotelmata, October 2000Approximately 630 plants are carnivorous, such as the Venus Flytrap (Dionaea muscipula) and sundew (Drosera species). They trap small animals and digest them to obtain mineral nutrients, especially nitrogen and phosphorus.Barthlott, W.; Porembski, S.; Seine, R.; Theisen, I. 2007. The Curious World of Carnivorous Plants: A Comprehensive Guide to Their Biology and Cultivation. Timber Press: Portland, Oregon.

Importance

The study of plant uses by people is called economic botany or ethnobotany.BOOK,weblink Economic Botany: A Comprehensive Study, Kochhar, S.L., 31 May 2016, Cambridge University Press, 9781316675397, Human cultivation of plants is part of agriculture, which is the basis of human civilization.BOOK,weblink Workplace Communication for the 21st Century: Tools and Strategies that Impact the Bottom Line [2 volumes]: Tools and Strategies That Impact the Bottom Line, Wrench, Jason S., 9 January 2013, ABC-CLIO, 9780313396328, Plant agriculture is subdivided into agronomy, horticulture and forestry.BOOK,weblink Report on the Agricultural Experiment Stations, United States Agricultural Research Service, 1903, U.S. Government Printing Office,

Food

(File:Harvest Time - geograph.org.uk - 747095.jpg|thumb|Mechanical harvest of oats.)Humans depend on plants for food, either directly or as feed for domestic animals. Agriculture deals with the production of food crops, and has played a key role in the history of world civilizations. Agriculture includes agronomy for arable crops, horticulture for vegetables and fruit, and forestry for timber.WEB, The Development of Agriculture,weblink National Geographic Society, National Geographic, 1 October 2017, 2016, yes,weblink 14 April 2016, About 7,000 species of plant have been used for food, though most of today's food is derived from only 30 species. The major staples include cereals such as rice and wheat, starchy roots and tubers such as cassava and potato, and legumes such as peas and beans. Vegetable oils such as olive oil provide lipids, while fruit and vegetables contribute vitamins and minerals to the diet.WEB, Food and drink,weblink Kew Gardens, 1 October 2017, yes,weblink" title="web.archive.org/web/20140328124344weblink">weblink 28 March 2014,

Medicines

Medicinal plants are a primary source of organic compounds, both for their medicinal and physiological effects, and for the industrial synthesis of a vast array of organic chemicals.WEB, Chemicals from Plants, Cambridge University Botanic Garden,weblink 9 December 2017, Note that the details of each plant and the chemicals it yields are described in the linked subpages. Many hundreds of medicines are derived from plants, both traditional medicines used in herbalismJOURNAL, Tapsell, L.C., Hemphill, I., Cobiac, L., Health benefits of herbs and spices: the past, the present, the future, Med. J. Aust., 185, 4 Suppl, S4–24, August 2006, 17022438, JOURNAL, Lai, P.K.; Roy, J., Antimicrobial and chemopreventive properties of herbs and spices, Curr. Med. Chem., 11, 11, 1451–1460, June 2004, 15180577, 10.2174/0929867043365107, Roy, and chemical substances purified from plants or first identified in them, sometimes by ethnobotanical search, and then synthesised for use in modern medicine. Modern medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. Plants used in herbalism include ginkgo, echinacea, feverfew, and Saint John's wort. The pharmacopoeia of Dioscorides, De Materia Medica, describing some 600 medicinal plants, was written between 50 and 70 AD and remained in use in Europe and the Middle East until around 1600 AD; it was the precursor of all modern pharmacopoeias.WEB,weblink Greek Medicine, National Institutes of Health, USA, 16 September 2002, 22 May 2014, BOOK,weblink Hefferon, Kathleen, Let Thy Food Be Thy Medicine, Oxford University Press, 2012, 46, 978-0199873982, BOOK,weblink Rooney, Anne, The Story of Medicine, Arcturus Publishing, 2009, 143, 978-1848580398,

Nonfood products

File:Timber DonnellyMills2005 SeanMcClean.jpg|thumb|Timber in storage for later processing at a sawmillsawmillPlants grown as industrial crops are the source of a wide range of products used in manufacturing, sometimes so intensively as to risk harm to the environment.WEB, Industrial Crop Production,weblink Grace Communications Foundation, 20 June 2016, 2016, Nonfood products include essential oils, natural dyes, pigments, waxes, resins, tannins, alkaloids, amber and cork. Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber, latex, lubricants, linoleum, plastics, inks, and gums. Renewable fuels from plants include firewood, peat and other biofuels.WEB, Industrial Crops and Products An International Journal,weblink Elsevier, 2016-06-20, BOOK, Cruz, Von Mark V., Dierig, David A., Industrial Crops: Breeding for BioEnergy and Bioproducts,weblink 2014, Springer, 978-1-4939-1447-0, 9 and passim, The fossil fuels coal, petroleum and natural gas are derived from the remains of aquatic organisms including phytoplankton in geological time.BOOK, Sato, Motoaki, Thermochemistry of the formation of fossil fuels, Fluid-Mineral Interactions: A Tribute to H. P. Eugster, Special Publication No. 2, 1990,weblink The Geochemical Society, Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. Wood is used not only for buildings, boats, and furniture, but also for smaller items such as musical instruments and sports equipment. Wood is pulped to make paper and cardboard.BOOK, Handbook of pulp, 1, Sixta, Herbert, 2006, Wiley-VCH, Winheim, Germany, 978-3-527-30997-9, 9, Cloth is often made from cotton, flax, ramie or synthetic fibres such as rayon and acetate derived from plant cellulose. Thread used to sew cloth likewise comes in large part from cotton.WEB, Natural fibres,weblink Discover Natural Fibres, 2016-06-20,

Aesthetic uses

File:Rose espalier Niedernhall.JPG|thumb|left|A rose espalierespalierThousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to historic gardens, national parks, rainforests, forests with colorful autumn leaves, and festivals such as Japan'sBOOK,weblink 12, Introduction to Japanese culture, Daniel, Sosnoski, Tuttle, 1996, 978-0-8048-2056-1, and America's cherry blossom festivals.WEB,weblink" title="web.archive.org/web/20160314055554weblink">weblink 14 March 2016,weblink History of the Cherry Blossom Trees and Festival, National Cherry Blossom Festival: About, National Cherry Blossom Festival, 22 March 2016, File:Luxor, West Bank, Ramesseum, column top decorations, Egypt, Oct 2004.jpg|thumb|Capitals of ancient Egyptian columns decorated to resemble papyrus plants. (at Luxor, Egypt)]]While some gardens are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. Arboretums and botanical gardens are public collections of living plants. In private outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Gardens may cultivate the plants in a naturalistic state, or may sculpture their growth, as with topiary or espalier. Gardening is the most popular leisure activity in the U.S., and working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities.{{cn|date=November 2018}}Plants may also be grown or kept indoors as houseplants, or in specialized buildings such as greenhouses that are designed for the care and cultivation of living plants. Venus Flytrap, sensitive plant and resurrection plant are examples of plants sold as novelties. There are also art forms specializing in the arrangement of cut or living plant, such as bonsai, ikebana, and the arrangement of cut or dried flowers. Ornamental plants have sometimes changed the course of history, as in tulipomania.WEB, Lambert, Tim, A Brief History of Gardening,weblink British Broadcasting Corporation, 21 June 2016, 2014, Architectural designs resembling plants appear in the capitals of Ancient Egyptian columns, which were carved to resemble either the Egyptian white lotus or the papyrus.BOOK, Wilkinson, Richard H., Richard H. Wilkinson, The Complete Temples of Ancient Egypt, 2000, Thames and Hudson, 978-0-500-05100-9, 65–66, Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.{{cn|date=November 2018}}

Scientific and cultural uses

File:Barbara McClintock (1902-1992).jpg|thumb|Barbara McClintock (1902–1992) was a pioneering cytogeneticist who used maizemaizeBasic biological research has often been done with plants. In genetics, the breeding of pea plants allowed Gregor Mendel to derive the basic laws governing inheritance,WEB, Mendel's Paper in English,weblink Roger B., Blumberg, and examination of chromosomes in maize allowed Barbara McClintock to demonstrate their connection to inherited traits.WEB, Barbara McClintock: A Brief Biographical Sketch,weblink WebCite, 21 June 2016, yes,weblink 21 August 2011, dmy-all, The plant Arabidopsis thaliana is used in laboratories as a model organism to understand how genes control the growth and development of plant structures.WEB, About Arabidopsis,weblink TAIR, 21 June 2016, NASA predicts that space stations or space colonies will one day rely on plants for life support.WEB, Engineering Life,weblink NASA, 21 June 2016, Ancient trees are revered and many are famous. Tree rings themselves are an important method of dating in archeology, and serve as a record of past climates.{{cn|date=November 2018}}Plants figure prominently in mythology, religion and literature. They are used as national and state emblems, including state trees and state flowers. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. The arrangement of flowers may be used to send hidden messages.{{cn|date=November 2018}}

Negative effects

Weeds are unwanted plants growing in managed environments such as farms, urban areas, gardens, lawns, and parks. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.{{cn|date=November 2018}}Plants may cause harm to animals, including people. Plants that produce windblown pollen invoke allergic reactions in people who suffer from hay fever. A wide variety of plants are poisonous. Toxalbumins are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including nicotine from tobacco, cannabinoids from Cannabis sativa, cocaine from Erythroxylon coca and opium from opium poppy. Smoking causes damage to health or even death, while some drugs may also be harmful or fatal to people.WEB,weblink cocaine/crack, WEB,weblink Deaths related to cocaine, Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.WEB,weblinkweblink" title="web.archive.org/web/20080215071055weblink">weblink 15 February 2008, Illegal drugs drain $160 billion a year from American economy, WEB,weblink The social cost of illegal drug consumption in Spain, September 2002,

See also

{{Wikipedia books|Plants}}{{div col|colwidth=30em}} {{div col end}}

References

{{Reflist|colwidth=30em}}

Further reading

General:
  • Evans, L.T. (1998). Feeding the Ten Billion – Plants and Population Growth. Cambridge University Press. Paperback, 247 pages. {{ISBN|0-521-64685-5}}.
  • Kenrick, Paul & Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D.C.: Smithsonian Institution Press. {{ISBN|1-56098-730-8}}.
  • Raven, Peter H.; Evert, Ray F.; & Eichhorn, Susan E. (2005). Biology of Plants (7th ed.). New York: W.H. Freeman and Company. {{ISBN|0-7167-1007-2}}.
  • Taylor, Thomas N. & Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. {{ISBN|0-13-651589-4}}.
  • JOURNAL, Trewavas A, 2003, Aspects of Plant Intelligence,weblink Annals of Botany, 92, 1, 1–20, 10.1093/aob/mcg101, 12740212, 4243628,


Species estimates and counts:
  • International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). IUCN Red List weblink.
  • JOURNAL, Prance G.T., 2001, Discovering the Plant World, Taxon, 50, 2, Golden Jubilee Part 4, 345–359, 10.2307/1223885, 1223885,

External links



Botanical and vegetation databases
{{Botany|state=expanded}}{{Plant classification}}{{Eukaryota classification|state=collapsed}}{{Nature nav}}{{Horticulture and Gardening}}{{Life on Earth}}{{Authority control}}{{Taxonbar|from=Q756}}

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